1. Field
The present specification generally relates to glass compositions and, more specifically, to chemically durable glass compositions which are suitable for use in pharmaceutical packaging.
2. Technical Background
Historically, glass has been used as the preferred material for packaging pharmaceuticals because of its hermeticity, optical clarity, and excellent chemical durability relative to other materials. Specifically, the glass used in pharmaceutical packaging must have adequate chemical durability so as to not affect the stability of the pharmaceutical compositions contained therein. Glasses having suitable chemical durability include those glass compositions within the ASTM standard ‘Type 1A’ and ‘Type 1B’ glass compositions which have a proven history of chemical durability.
Although Type 1A and Type 1B glass compositions are commonly used in pharmaceutical packages, they do suffer from several deficiencies. Foremost is the tendency of these glasses to phase separate. Specifically, the glass tends to separate on a fine microscopic scale into an alkali borate phase and a silica rich phase. This phase separation may be a precursor to the glass flakes and de-lamination phenomena that have been reported in such glasses.
A second deficiency is that the low levels of alkali and alumina in Type 1A and Type 1B glass compositions result in only a minimal ability to ion exchange and strengthen these glasses. As a result, pharmaceutical packages made from Type 1A and 1B pharmaceutical glasses offer poor resistance to damage from mechanical events such as impacts and scratches.
Accordingly, a need exists for glass compositions which are chemically durable and susceptible to chemical strengthening by ion exchange for use in glass pharmaceutical packages and similar applications.